Emily Lakdawalla • Jul 25, 2018
Hayabusa2 descends from Home Position to take its first close look at Ryugu
Hayabusa2 arrived at Ryugu on June 27, maintaining a standoff distance of 20 kilometers for its initial surveys of the kilometer-sized asteroid and its shape. They call the 20-kilometer standoff distance "Home position," and have established confidence in their ability to hold stably at that position.
With home base -- also known as the "Box A" position -- established, the spacecraft can now take two kinds of excursions. Taking the asteroid as being "down" from Hayabusa2 (that is, in the -Z direction)*, the spacecraft can now venture to all sides of Home position, 10 kilometers in the X or Y directions. Hayabusa2 will be able to view the asteroid from different angles and under different lighting conditions. Hayabusa2 navigators refer to this region, 10 kilometers in X and Y directions, as "Box B."
Another maneuvering zone contains Box A and allows Hayabusa2 to descend to within 5 kilometers of the asteroid's surface. This is called "Box C." Hayabusa2 left Box A for the first time on July 17, arrived at the bottom of Box C on July 20, spent a day there, and returned to Home position in Box A on July 25. The images that Hayabusa2 took from the bottom of Box C reveal meter-sized boulders and will help the team begin to select potential landing sites.
* What defines the precise "down" direction for Hayabusa2, though? I had initially assumed that "down" was "away from the Sun," but this is NOT true. The Hayabusa2 team actually defines "down" as "away from Earth," which makes sense as a coordinate system when your mission's biggest challenge is navigating precisely around a low-gravity object. From two-way light-time measurements, the navigators can very precisely track Hayabusa2's change in distance with respect to the asteroid.
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